package com.sidianzhong.sdz.utils;

public class CodeProcess {
	
	private  final static int LEN = 6;
	//验证码字符列表
	private  final static char STUFFS[] = { 	
			'A','B','C','D','E','F','G','H',
			'I','J','K','L','M','N','P','Q',
			'R','S','T','U','V','W','X','Y',
			'1','2','3','4','5','6','7','8'};
	
	private  final static int PERMUTATION;
	private  final static int MAX_COMBINATION;
	
	static {
		PERMUTATION = permutation(LEN);
		MAX_COMBINATION = combination(STUFFS.length,LEN);
	}
	
	private static  int combination(int n,int m) {
		int com = 1;
		for(int i = n - m + 1; i <= n ; ++i) {
			com *= i;
		}
		for(int i = 2; i <= m ; ++i ) {
			com /= i;
		}
		return com;
	}
	
	private static  int permutation(int n) {
		int per = 1;
		for(int i = 2; i <= n ; ++i) {
			per *= i;
		}
		return per;
	}
	
	public static int decode(String code) {
		if(code.length() != LEN) {
			throw new RuntimeException("invalid code");
		}
		char[] chars = new char[LEN];
		for(int i = 0; i < LEN;++i) {
			chars[i] = code.charAt(i);
		}
		int com = combination(chars);
		int per = permutation(chars);
		return com * PERMUTATION + per;
	}
	
	public  static String encode(int val) {
		int com = val / PERMUTATION;
		if(com >= MAX_COMBINATION) {
			throw new RuntimeException("id can't be greater than 652458239");
		}
		int per = val % PERMUTATION;
		char[] chars = combination(com);
		chars = permutation(chars,per);
		return new String(chars);
	}
	
	private static char[] combination(int com){
		char[] chars = new char[LEN];
		int start = 0;
		int index = 0;
		while (index < LEN) {
			for(int s = start; s < STUFFS.length; ++s ) {
				int c = combination(STUFFS.length - s - 1, LEN - index - 1);
				if(com >= c) {
					com -= c;
					continue;
				}
				chars[index++] = STUFFS[s];
				start = s + 1;
				break;
			}
		}
		return chars;
	}
	
	private static char[] sort(char[] src) {
		char[] sort = new char[src.length];
		int index = 0;
		for(int i = 0; i < STUFFS.length;++i) {
			if(find(src, STUFFS[i]) != -1) {
				sort[index++] = STUFFS[i];
			}
		}
		return sort;
	}
	
	private static int combination(char[] chars) {
		int[] offset = new int[LEN];
		char[] sort = sort(chars);
		for(int i = 0; i < sort.length;++i) {
			offset[i] = find(STUFFS, sort[i]);
			if(offset[i] == -1) {
				throw new RuntimeException("invalid code");
			}
		}
		int com = 0;
		for(int i = 0;i < offset.length;++i) {
			if(i == 0) {
				if(offset[0] == 0) {
					continue;
				}
				for(int n = 0; n < offset[0];++n) {
					com += combination(STUFFS.length -  n - 1, LEN - 1);
				}
				continue;
			}
			
			if(offset[i] - offset[i - 1] <= 1) {
				continue;
			}
			
			for(int n = offset[i-1] + 1; n < offset[i];++n) {
				com += combination(STUFFS.length -  n - 1, LEN - i - 1);
			}
		}
		
		return com;
	}
	
	private static char[] permutation(char[] chars,int per){
		char[] tmpchars = new char[chars.length];
		System.arraycopy(chars, 0, tmpchars, 0, chars.length);
		int[] offset = new int[chars.length];
		int step = chars.length;
		for(int i = chars.length -1;i >= 0;--i) {
			offset[i] = per % step;
			per /= step;
			step --;
		}
		
		for(int i = 0; i < chars.length;++i) {
			if(offset[i] == 0)
				continue;
			char tmp = tmpchars[i];
			tmpchars[i] = tmpchars[i - offset[i]];
			tmpchars[i - offset[i]] = tmp;
		}
		
		return tmpchars;
	}
	
	private static int find(char[] chars,char ch) {
		for(int i = 0;i < chars.length;++i) {
			if(chars[i] == ch) {
				return i;
			}
		}
		return -1;
	}
	
	private static int permutation(char[] chars){
		char[] sort = sort(chars);
		int[] offset = new int[chars.length];
		for(int i =chars.length -1;i >=0;--i ) {
			int f = find(chars, sort[i]);
			offset[i] = i - f;
			char tmp = chars[i];
			chars[i] = chars[i - offset[i]];
			chars[i - offset[i]] = tmp;
		}
		int per = 0;
		int step = 1;
		for(int i = 0; i < offset.length;++i ) {
			per = per * step + offset[i];
			step++;
		}
		return per;
	}
/*
	public static void main1 (String args[]){
		Random random = new Random();
		for(int i = 0; i < 100000;++i) {	
			int id = random.nextInt(652458240);	
			String code = encode(id);	
			int nid = decode(code);	
			System.out.println(  id + " -> " + code + " -> " + nid);
			}
 
	}*/
}
